PART C (Answer any two from the following)

7. a) Describe the principle of operation of helical antenna under (i) normal mode and (ii)
axial mode of operation. What are its application (10M)

b) Explain the terms critical frequency and maximum usable frequency of an
ionosphere layer (4M) c) Derive the field strength of tropospheric wave. (6M)

8. ೩) Write short notes on (i) patch antenna

(ii) log periodic antenna (10M)
b) Explain briefly the ionospheric abnormalities and absorption. (10M)
9. a) Explain the principle of smart antenna (8M)

b) Write short notes on (i) super refraction

(11) tropospheric scatter propagation (12M)